Vanadium (IV) dioxide, VO2, has been a subject of intense scrutiny because it undergoes a reversible semiconductor-to-metal phase transition at a relatively low temperature (68° C.) (see references 1, 2 and 3). This leads to dramatic changes in its electrical and optical properties in the near infrared (IR) (see references 4 and 5) that make it a useful material in several applications including smart windows, sensors, and optical storage devices (see reference 6). In addition to being a thermochromic material VO2 is also electrochromic; that is, the phase transition can be induced by passing a current through the material by means of a voltage application.
Similarly, the phase transition can be induced by irradiating the sample with laser light provided the photon energy exceeds the band gap of the material (˜0.6 eV; H. W. Verleur et al, Rev. Mod. Phys. 40, 737 (1968)). This makes VO2 thin films appropriate for use as an optical limiter. Vanadium oxides can adopt many stoichiometries corresponding to different vanadium oxidation states. The preparation of stoichiometric VO2 therefore requires stringent experimental control over the oxidation process in order to obtain the desired oxygen stoichiometry and crystallinity (see references 6 and 7). Pan et. al. showed that the sol-gel method can be easily used to fabricate VO2 thin film from vanadium oxyacetylacetonate (VO(acac)2) methanol solution (see reference 8). However, the inherent shortcoming to this method is the rapid oxidation of VO(acac)2 in methanol solution (see reference 9). This drawback has impacted negatively on the economical development of thermochromic devices based on VO2.
Therefore there is a need to provide a simple chemistry approach that stabilizes vanadium oxyacetylacetonate against oxidation in solution.